English for students of Physics_Unit 10

66 Unit Ten ENERGY READING PASSAGE Friction, Internal energy, and Heat Toss your keys along the floor, they’ll skitter along for a bit as friction does negative work on them, reducing their kinetic. Quickly, the keys come to rest, and the kinetic energy you gave them is gone. But in this case they can’t turn around (as they did when you picked them up), gather speed from the same frictional force that acted to slow them, and jump back into your hand with the same kinetic energy. Once the motion stops, the friction stops, and it can not restore the kinetic energy of the keys as gravity is able to do. Frictional forces don’t store energy in the form of potential energy. But all the kinetic energy that you gave the keys when you tossed them doesn’t just disappear. The keys skid across the surface of the floor, scraping and catching. The affected surface molecules of the keys and the floor are pushed through some tiny distance, giving them extra kinetic energy. Molecules throughout any solid object bounce around in all directions even though they are held in place by their bonds with the molecules around them. When molecules of the keys and the floor strike each other, however, they bounce around even faster. The affected molecules slam into the nearest neighbors (in all directions) and these, too, move a bit faster. All the organized kinetic energy the keys had just before they hit the floor disappears, and most of it scatters aimlessly among the molecules. That chaotic energy now is part of the energy stored in the matter. We call that energy the internal energy of the keys and the floor. The internal energy in matter can be thought of as the sum of the kinetic and potential energies of all of its molecules including, as we see, energy called chemical, gravitational, and nuclear, and energy associated with the presence of mass itself. When the molecules of matter move faster, the matter becomes warmer, that is, its temperature increases. But all the keys’ original kinetic energy doesn’t just go to raise the temperature of the keys and the floor. A portion of that energy goes into work that deforms, or scratches, the keys and the floor, and some of the energy even goes into making sound. But the important point here is that whenever frictional forces do work, some of the work goes into increasing the internal energy of matter, and this internal energy spreads out, making it much less effective at producing work than, say, the organized kinetic energy of a moving object. For example, in a car’s engine some of the potential energy stored in the gasoline or diesel fuel turns into random kinetic energy of the molecules. The heated gases push pistons 67 downward, but all of that released energy can not be converted to work on the pistons. The energy the pistons get from those hot gases is only about 25 percent of the energy released from the chemical bonds. The rest? Some goes into raising the temperature of the cylinder walls and the piston, and that part spreads outward, doing no useful work. Some leaves with the still-hot gases that escape through the exhaust system of the car, once again doing no useful work. The efficiency of a machine (or animal or any other energy processor) is defined as work done/energy used. The efficiency of a car’s engine is 0.25 if 25 percent of the energy released by the fuel goes into work on the car. Because of frictional forces and the loss of energy through the exhaust gases and to the cylinder walls, an automobile’s efficiency could never be equal to 1 (or 100 percent). The same is true for us, where a large percentage of energy released in metabolism goes to keep our internal energy high – it goes to keep us warm. Almost every time anything moves through some distance, friction from some source does work and transforms some kinetic energy into internal energy. As the internal energy spreads, or is even transferred to another body, we say there is a flow of heat or heat transfer. Heat refers to the part of an object’s internal energy that is moving because of difference in temperature. (Often the energy that can move this way is called heat energy, or thermal energy, but strictly speaking heat is not stored energy. Heat is energy that is moving from one place to another place, increasing or decreasing an object’s internal or stored energy.). But the connections between work done by friction and internal energy and heat were not fully understood until the 1840s. Once that connection was made, it quickly led to an important insight into nature. That is the law of conservation of energy: In every interaction of any kind, the total energy afterward is always the same as the total energy to begin with. (Adapted from Physics, an introduction by Jay Bolemon, 1989) READING COMPREHENSION Exercise 1: Answer the following questions by referring to the reading text. 1. What’s the property of molecules in a solid object? ………………………………………………………………………………………… ……………………………………………………………………………… 2. What’s internal energy of a matter? ………………………………………………………………………………………… ……………………………………………………………………………… 3. What happens when frictional forces do work? ………………………………………………………………………………………… ……………………………………………………………………………… 4. In your own words, define the efficiency of a machine? 68 ………………………………………………………………………………………… ……………………………………………………………………………… 5. What is heat? ………………………………………………………………………………………… ……………………………………………………………………………… Exercise 2: Contextual reference (Dealing with words in bold type) 1. “it” in line 6 refers to a. the motion b. thee friction 2. “Them” in line 12 refers to a. the affected surface molecules of the keys b. the affected surface molecules of the keys and the floor 3. “These” in line 16 refers to a. the affected molecules b. the nearest neighboring molecules 4. “Its” in line 24 refers to a. of the molecule b. of the matter 5. “that energy” in line 26 refers to a. the key’s original kinetic energy b. the floor’s kinetic energy 6. “The heated gases” in line 33 refers to a. potential energy in gasoline and fuel b. random kinetic energy of the molecules 7. “some” in line 38 refers to a. some of the energy released from the chemical bonds b. the energy that spreads out 8. “it” in line 56 refers to a. nothing b. the connection between work done by friction and internal energy and heat Exercise 3: Fill in the blanks with words/phrases from the reading text 69 1. Friction stops when motion stops but can not restore the ……………………. of the keys tossed along the floor as gravity can. 2. Frictional forces don’t store energy in the form of……………… .……………. 3. All molecules in a ………….bounce around in all directions. 4. ………… ……………of matter equals to the sum of the kinetic energy and potential energy of all of its molecules plus some other forms of energies. 5. A raise in ……………of a matter results from the faster movement of its molecules. 6. Some of …………….…………… done frictional forces helps increase the internal energy of matter. 7. Much of the energy released from the …………………………….of gasoline or diesel fuel in a car’s engine does no useful work. 8. …………… ………………of a car’s engine is defined by the percent of the energy released by the fuel that goes into work on the car. GRAMMAR IN USE Present participle with some special functions A present participle phrase is the one of which the central element is a present participle formed as an –ing form of verb Example: The phosphor gas rose up into the air, making specks of light. You have learnt the use of present participle in replacing relative clause and clause of reason with active meaning. The following will present some others commonly applied in science writing. 1. Present participle phrase (also known as an –ing clause) is used to give an explanation Example: The molten iron, having been in contact with the coke in the lower part of the furnace, contains several percent of dissolved carbon. In the above example, the participle phrase is used to give an explanation for the action mentioned in the main clause. 2. Present participle phrase is used to mention something as a part of the action mentioned in the main clause: that can be either an addition or a result or consequence of that action. Example: 70 a. Toss your keys along the floor, they’ll skitter along for a bit as friction does negative work on them, reducing their kinetic. (consequence) b. The keys skid across the surface of the floor, scraping and catching. (addition) c. The affected surface molecules of the keys and the floor are pushed through some tiny distance, giving them extra kinetic energy. (result) Note: If the subject of the participle phrase is the same as the subject of the main clause, it is omitted, as in the above examples. However, if the two objects are different, both of them must be mentioned. Example: Wheels of different diameters are engaged to each other, the smaller ones making more revolutions. 3. Present participle is used to replace an adverbial clause of time with active verb phrase (or shorten an adverbial clause of time with active verb phrase to a present participle phrase of time) First, we should recall of what an adverbial clause of time is like: In form, an adverbial clause of time is the one which starts with a time conjunction. In grammar, it is a subordinate (dependent) clause. In meaning, it sets a time reference for the action mentioned in the main (independent) clause. Example: a. Once the motion stops, the friction stops, and it can not restore the kinetic energy of the keys as gravity is able to do. b. All the kinetic energy that you gave the keys when you tossed them doesn’t just disappear. c. When molecules of the keys and the floor strike each other, they bounce around even faster. d. When the molecules of matter move faster, the matter becomes warmer. e. The important point here is that whenever frictional forces do work, some of the work goes into increasing the internal energy of matter, . f. Almost every time anything moves through some distance, friction from some source does work and transforms some kinetic energy into internal energy. An –ing clause can replace an adverbial clause of time in this way: We retain the conjunction of time, in general, and reduce the verb in the clause to its –ing form. Normally, this can be done with the sentence in which the subject in the time clause is 71 the same as that in the main clause. However, in many cases, especially in science writing, these are different. Thus, we have to retain the subject regardless of the difference. Therefore, the above sentences can be rewritten in this way: a. Once the motion stopping, the friction stops, and it can not restore the kinetic energy. b. All the kinetic energy that you gave them when tossing them doesn’t just appear. c. When striking each other, the molecules of the keys and the floor bounce around even faster. d. When the molecules of matter moving faster, the matter becomes warmer. e. The important point here is that whenever frictional force doing work, some of the work goes into increasing the internal energy of that matter. f. Almost every time anything moving through some distance, friction from some source does work and transforms some kinetic energy into internal energy. Note: that you may have an impression that the clause is not at all shortened (reduced) in length (or in number of words). However, the word ‘shorten’ or ‘reduce’ just implies the reduction in grammatical aspect, i.e. we reduce a clause into a phrase. That’s why the use of the word ‘replace’ is quite reasonable for the cases. To emphasize the completion of an action with respect to another, we use the perfect participle: having done Example: Having carefully prepared, he successfully detected the questionable element in the compound. In such a case, we have more than one way to express the relationship between two actions (one is conducted before the other). You can write the sentence in these ways: a. After he had carefully prepared, he successfully detected the questionable element in the compound. b. After preparing carefully, he successfully detected the questionable element in the compound. c. After having carefully prepared, he successfully detected the questionable element in the compound. d. Preparing carefully, he successfully detected the questionable element in the compound. In which: 72 Sentence (a) is the most neutral in style and the most usual of these patterns in everyday speech. (b) is also usual, although a little more formal. (c) is less usual because after and having both repeat the idea of one action following the other. (d) and the original one are rather literary. (d) also means that the two actions were very close in time. PRACTICE Exercise 1: Combine each of the following pairs of sentences using an –ing clause, state in each case the function of the -ing clause 1. Only the magnitude of this variable force changes, not its direction. Moreover, its magnitude changes with the position of the particle. ………………………………………………………………………………………… ……………………………………………………………………………… 2. In the limit, we let the strip width approach zero. The number of strips then becomes infinitely large. ………………………………………………………………………………………… ……………………………………………………………………………… 3. We stretch the spring by pulling the block to the right. In reaction, the spring pulls on the block toward the left, in the direction that will restore the relaxed state. ………………………………………………………………………………………… ……………………………………………………………………………… 4. The length of the spring is one of several factors that determine the spring constant k. Thus, the length is in those equations implicitly. ………………………………………………………………………………………… ……………………………………………………………………………… 5. In the British system, the unit of power is the foot-pound per second. Often the horse power is used. ………………………………………………………………………………………… ……………………………………………………………………………… 6. At low speeds, the two formulas merge. They yield the same result. ………………………………………………………………………………………… ……………………………………………………………………………… 7. We apply Newton’s laws of mechanics only in inertia reference frames. These frames move at constant velocity. ………………………………………………………………………………………… ……………………………………………………………………………… 73 8. For some physical quantities, observers in different inertia reference frames will measure the exact same values. In Newtonian mechanics, these invariant quantities (as they are called) are force, mass, acceleration and time. ………………………………………………………………………………………… ……………………………………………………………………………… 9. Some quantities (such as mass, force, acceleration, and time in Newtonian) are variant. That is, they have the same numerical values when measured in different inertia reference frames. ………………………………………………………………………………………… ……………………………………………………………………………… 10. Thermal energy is said to be an internal energy of an object. It involves random motions of the atoms and molecules within an object. ………………………………………………………………………………………… ……………………………………………………………………………… 11. The work W f done on the block by f k is not entire amount of dissipated energy, but only the part that is transferred from the block to the floor. The rest of the dissipated energy remains within the block as thermal energy. ………………………………………………………………………………………… ……………………………………………………………………………… 12. Although the mechanical energy of the block is not conserved, the sum of the mechanical energy of the block and the thermal energy of the block and the floor is conserved. That sum is called the total energy E tot of the block-floor system, and our new conservation principle is called the law of conservation of energy. ………………………………………………………………………………………… ……………………………………………………………………………… ………………………………………………………………………………………… ……………………………………………………………………………… 13. Power is the rate at which work is done by a force. In more general sense, it is the rate at which energy is transferred by a force from one form to another. ………………………………………………………………………………………… ……………………………………………………………………………… 14. In 1905, Einstein showed that as a consequence of his theory of special relativity, mass can be considered to be another form of energy. Thus the law of conservation of energy is really the law of conservation of mass-energy. ………………………………………………………………………………………… ……………………………………………………………………………… 74 15. A force is conservative if its work on a particle moving between two points does not depend on the path taken by the particle. The gravitational force (weight) and the spring force are conservative forces; the kinetic frictional force is non-conservative force. ………………………………………………………………………………………… ……………………………………………………………………………… ………………………………………………………………………………………… ……………………………………………………………………………… Exercise 2: Reduce the adverbial clause of time in each of the following sentences 1. Note that when we change the variable from x to v we are required to express the limits on the integral in terms of the new variable. ………………………………………………………………………………………… ……………………………………………………………………………… 2. When the tomato returns to the launch point, it again has speed v 0 and kinetic energy 2 0 2 1 mv . ………………………………………………………………………………………… ……………………………………………………………………………… 3. As the particle moves from point y 1 to point y f , its weight mg does work on it. ………………………………………………………………………………………… ……………………………………………………………………………… 4. When the atom reaches an excited state, it does not stay there but quickly de-excites by decreasing its energy, either in a collision or by emitting light. ………………………………………………………………………………………… ……………………………………………………………………………… 5. While we illustrate the law of conservation of mechanical energy, we persistently repeat: “in the absence of friction; if there were no friction…” ………………………………………………………………………………………… ……………………………………………………………………………… 6. When heat comes from a hot water bottle, the water in the bottle loses internal energy equal to the energy the heat carries away. ………………………………………………………………………………………… ……………………………………………………………………………… 7. When Joule did experiments to warm water with paddle wheels, he wanted to see precisely how much thermal energy came from a given amount of work. 75 ………………………………………………………………………………………… ……………………………………………………………………………… 8. Once the glass of tea reaches the temperature of its surrounding, it is at thermal equilibrium. ………………………………………………………………………………………… ……………………………………………………………………………… 9. When water evaporates, it absorbs a lot of energy without a change in temperature. ………………………………………………………………………………………… ……………………………………………………………………………… 10. When a warm solid surface touches a cold solid surface, many of the molecules touch, and the faster vibrating molecules will pass vibrational energy along to those vibrating slower. ………………………………………………………………………………………… ……………………………………………………………………………… PROBLEM – SOLVING Paragraph building Task one From the prompts given, build up sentences with the addition of the supplementary material above each set. Delete the words /phrases in Italic 1. AS/ACCELERATES/ MIDPOINT /,/ DECREASES/,/AND/INCREASES it speeds up towards the center of the oscillation its potential energy reduces its kinetic energy goes up . 2. AT THE MOMENT/, /IT when you release the mass the mass has potential energy 3. REMAINS CONSTANT [...]... energy In 1905 Albert Einstein showed, in his special theory of relativity, that mass and energy are equivalent Consequently, the separate laws of conservation of mass and of energy found a more general and exact formulation as the law of conservation of the total of mass and energy (Adapted from different souces) 79 Task two: Vietnamese - English translation 1 Mỗi một động cơ có một công suất N nhất... the day of the year, the time of day, and the latitude of the collection point Furthermore, the amount of solar energy that can be collected depends on the orientation of the collecting object Natural transformation of solar energy .Natural collection of solar energy occurs in the earth’s atmosphere, oceans, and plant life Interactions between the sun’s energy, the oceans, and the atmosphere, for example,... because a force that acts on a body has the potential to perform work on that body Thế năng Power (n): the rate of doing work or using energy Power is the ratio of work done (or energy used) to the amount of time required to do that work (or to use that energy) Công suất Radiation (n): the transfer of heat by radiation Truyền nhiệt bằng phát xạ Thermal equilibrium (n): property of a system all parts of which... beginning of time in the Universe The wavelength distribution of radiation corresponds to a temperature of just 2.7 K above absolute zero 5 The law of conservation of mass may be considered valid for chemical reactions (the changes in mass, equivalent to the produced or absorbed energy, are not measurable), but (as was later determined) it is not valid for nuclear reactions, where a much larger quantity of. .. population of prey and predators, the output and input in chemical reactions, and the generation of light and heat from stars It is the conservation of energy that makes the concept of energy so valuable to describe changes in nature If only part of the energy can actually be measured in a situation, the rest can be deduced from the application of this law Energy has been called the “common denominator” of. .. matter or energy with its surroundings and can therefore attain a state of thermodynamic equilibrium Hệ cô lập Kinetic energy (n): the energy of motion of a body A measure of a moving body’s 1 2 ability to do work, related to its mass and speed through the relation mv0 Động năng 2 Potential energy due to gravity (n): the measure of the potential of gravity to do work on an object Near earth’s surface,... radiation is part of the electromagnetic spectrum It consists of electromagnetic waves whose wavelengths are longer than those of visible light For every cold object, the wavelengths may be very long, reaching into the microwave part of the spectrum Astronomers have found evidence of such microwave radiation pervading the Universe This is called the microwave background, and is the remnant of radiation... used to generate most of the electricity in the United States Nuclear power plants and hydroelectric plants (where potential energy of elevated water drives turbines) account for less than 15 percent of the electrical power in the United States 3 Energy and energy changes are used to describe the exercise of joggers, the production and output of thunderstorms, the destructive power of earthquakes, the... have been used for centuries to turn windmills Modern applications of wind energy use strong, light, weatherresistant aerodynamically designed wind machines that, when attached to generators, produce electricity for local, specialized use or as part of a community or regional network of electric power distribution Approximately 30 percent of the solar energy reaching the outer edge of the atmosphere... energy Sự truyền, dẫn nhiệt Convection (n): the transfer of heat by a current of moving fluid such as air or water Sự đối lưu Efficiency (n): the ratio of work a system does to the energy it uses Hiệu suất Heat: energy moving by conduction Nhiệt lượng Internal energy (n): the energy stored within a matter in the forms of kinetic and potential energies of its molecules or atoms, including the mass itself . ………… of matter equals to the sum of the kinetic energy and potential energy of all of its molecules plus some other forms of energies. 5. A raise in ………… of. consequence of his theory of special relativity, mass can be considered to be another form of energy. Thus the law of conservation of energy is really the law of